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landing speed into account. The parameters described in this section affect
Body Vertical keys created in this manner.
Airborne Dynamics
With footsteps, each airborne period always begins and ends with Body
Horizontal and Body Vertical keys. These keys define the position of the biped
at lift-off and touchdown.
When the biped is airborne and Biped Dynamics is turned on, the vertical
motion is governed by physically based dynamics. Its airborne trajectory is
based on the current gravity setting, the height of the Body Vertical key at
lift-off and touchdown, and the amount of time in the air.
By default, there is no Body Vertical key at the peak of the biped's trajectory;
the biped's peak airborne height is calculated and enforced automatically. You
cannot, for example, set a Body Vertical key at the peak of an airborne
trajectory and move the biped up or down. If you attempt to do so, the biped
will snap back to its original airborne height. Although this will cause a
Body
Vertical key
on page 4196to appear on the Track Bar and in Track View, the key
will have no effect on the biped's airborne height.
Gravity and Timing
In reality, the length of time a person, animal or insect stays in the air during
a jump is based on two factors:
How high the creature jumps, which in turn is based on how hard the
creature pushes with its legs at the start of the jump. The creature's weight
has no bearing on the height of the jump, except to affect its ability to
give a good push at the start. A very light character might be taken by the
wind and thus stay in the air longer, but that circumstance is not part of
the gravitational equation.
The gravitational pull of the planet from which the creature jumps.
From these two factors, you can calculate how long the creature will stay in
the air. You can also perform this calculation backward; if you know how long
the creature was in the air and the gravitational equation for the planet, you
can figure out how high it jumped.
4218 | Chapter 17 character studio